1. Technical Field
The present disclosure relates to a damping force variable valve and a shock absorber including the same, and more particularly, to a damping force variable valve, which includes a spool rod having an efficiently configured structure that substantially resists twisting thereof, and a shock absorber including the same.
2. Description of the Related Art
Generally, a shock absorber absorbs or relieves sudden shocks or vibrations and is installed to, for example, a vehicle to ensure driving stability and ride comfort by quickly absorbing vibration of a spring caused by a road surface while the vehicle travels on the road.
Such a shock absorber provides a low damping force to enhance ride comfort by absorbing vibration due to unevenness of the road surface during ordinary travel of the vehicle, and provides a high damping force to enhance handling stability by suppressing a posture change of a vehicle body when the vehicle turns, accelerates, decelerates, travels at high speed, and other movements resulting in a vehicle posture change.
In recent years, the shock absorber has been developed to incorporate a damping force variable valve at one side thereof for properly adjusting damping characteristics according to road surface conditions and driving conditions of a vehicle in order to enhance ride comfort or handling stability.
To this end, conventional shock absorbers are provided with a damping force variable valve 70 as shown in FIG. 1 at one side of a base shell of the shock absorber to adjust the damping force.
FIG. 1 is a side sectional view of a conventional damping force variable valve. In a damping force variable valve 10, a spool 30 controls communication of a fluid while operating in a poppet valve manner with respect to a spool rod 20. As shown therein, the damping force variable valve 10 includes a solenoid unit 40, a spool rod 20, a spool 30, a lower retainer 22, a main disc 26, and an upper retainer 24.
The solenoid unit 40 is secured at an upper end thereof to a lower end of a valve housing 12 coupled to an outside of the shock absorber, and includes a bobbin 42 and a push rod 44 within an operating block 46. The push rod 44 moves up and down according to change in electric current or power applied to a coil wound around the bobbin 42. Further, the solenoid unit 40 is coupled at a lower end thereof to a cover 48.
The spool rod 20 has a hollow cylindrical shape and is disposed on an upper end of the operating block 46 of the solenoid unit 40. The spool rod 20 is provided at an upper end thereof with a plug 21, and a coil spring 21a is internally disposed between the plug 21 and the spool 30 to force the spool 30 to closely contact the push rod 44. Further, a plurality of connecting ports 20a, 20b and 20c through which the fluid flows are formed through the spool rod 20.
The lower retainer 22 is disposed around a periphery of the spool rod 20 and is formed therein with an inflow path 22a, a discharge path 22b, and a bypass path 22c. 
Further, the main disc 26 is disposed to cover the inflow path 22a from a rear side of the lower retainer 22 and directly faces against operating oil passing through the inflow path 22a, thereby generating damping force.
Further, the upper retainer 24 is installed on top of the lower retainer 22 and forms a guide channel which guides the fluid from a high pressure chamber of the shock absorber into the lower retainer 22. Additionally, a nut 28 is provided on an upper periphery of the spool rod 20 to fasten the lower retainer 22 thereto.
The spool rod 20 is formed at one end thereof with a male thread portion, and the operating block 46 is formed at a middle portion thereof with a female thread portion such that the spool rod 20 and the operating block 46 can be detachably secured to each other.
However, the conventional damping force variable valve 10 and the shock absorber including the same can suffer twisting when the spool rod 20 and the operating block 46 are threadedly coupled to each other, so that the spool 20 cannot move up and down smoothly. Further, the conventional damping force variable valve 10 has a complicated internal structure, generates a scattered damping force according to an assembled state of respective components, and cannot provide a desired damping force at low speed due to initial resistance. Moreover, assembling the respective components of the conventional damping force variable valve 10 is difficult and requires substantial time, thereby lowering productivity of final products.